Often before a movie screening, trailers of future movies will be shown. This is generally considered the best way to advertise a future movie. First, the audience has shown by its presence that it is willing and able to pay to go to a theatre. Second, the immersive effect of the large screen and the attendant sound system is more effective than television ads or billboards or other traditional means in conveying an anticipated future viewing experience. This is especially germane because of the increasing effectiveness of various automatic ad skipping methods for television. Hence while any type of ads could be shown in the theatre before the main screening, in practice these are mostly movie trailers.
But a perennial problem for the theatre and the studios has been how to quantify this presentation of trailers. Traditionally, before the prevalence of cellphones, the patron would have to leave the theatre at the end of the movie, remember the trailers and later decide to go to a theatre, and not necessarily the same theatre chain, to buy a physical ticket to a movie she saw in a trailer. To simplify this for her, some theatres offer a means of buying electronic tickets on the Internet. She can do this from her home computer or mobile device. But when she does so, the theatre does not know in general that she has been influenced by seeing a trailer. It might ask her in the web page where she places her order, but she might decline to answer. Also, by putting extra items in a web page or sequence of web pages, this has the risk of confusing the visitor and thus lessening the chance that she successfully completes a purchase.
Even if she were to use her cellphone to buy a ticket while in the theatre watching the trailer, it is noteworthy that the theatre usually will not know that she is in the theatre. Its web server will see an Internet address for a web query (that originated from her device). But that address might be a temporary one dynamically assigned by her wireless provider from a set of addresses owned by the provider. Or, on the Internet network, the query might originate from the wireless provider's gateway machine, that sits on both the Internet and the provider's internal network. Any geographic data publicly accessible and associated with that Internet address will be a location of the wireless provider. In general, that location will likely be somewhere in the same city of the theatre.
In principle, the theatre could try to address this by its web server knowing accurately the times at which it has shown trailers. When it gets an Internet purchase for a movie during or soon after its trailer was shown, it might infer that the buyer was in the theatre. But often the web server is for all the theatres in that theatre chain. And each theatre could be a multiplex, with several screens. For this to be tried, the chain needs accurate temporal records of all its screenings.
Readers may note that the lack of ability to measure the effectiveness of trailers is common to most traditional forms of ads, like those in magazines, billboards and television.